Deploying a scalable Jenkins cluster with Docker and Rancher

Containerization brings several benefits to traditional CI platforms where builds share hosts: build dependencies can be isolated, applications can be tested against multiple environments (testing a Java app against multiple versions of JVM), on-demand build environments can be created with minimal stickiness to ensure test fidelity, Docker Compose can be used to quickly bring up environments which mirror development environments. Lastly, the inherent isolation offered by Docker Compose-based stacks allow for concurrent builds — a sticking point for traditional build environments with shared components.

One of the immediate benefits of containerization for CI is that we can leverage tools such as Rancher to manage distributed build environments across multiple hosts. In this article, we’re going to launch a distributed Jenkins cluster with Rancher Compose. This work builds upon the earlier workby one of the authors, and further streamlines the process of spinning up and scaling a Jenkins stack.

Our Jenkins Stack

For our stack, we’re using Docker in Docker (DIND) images for Jenkins masterand slaverunning on top of Rancher compute nodes launched in Amazon EC2. With DIND, each Jenkins container runs a Docker daemon within itself. This allows us to create build pipelines for dockerized applications with Jenkins.

Prerequisites

AWS EC2 account

IAM credentials for docker machine

Rancher Server v0.32.0+

Docker 1.7.1+

Rancher Compose

Docker Compose

Setting up Rancher

Step 1: Setup an EC2 host for Rancher server

First thing first, we need an EC2 instance to run the Rancher server. We recommend going with Ubuntu 14.04 AMI for it’s up-to-date kernel. Make sure to configure the security group for the EC2 instance with access to port 22 (SSH) and 8080 (rancher web interface):

Once the instance starts, the first order of business is to install the latest version of Docker by following the steps below (for Ubuntu 14.04):

sudo apt-get update

curl -sSL https://get.docker.com/ | sh (requires sudo password)

sudo usermod -aG docker ubuntu

Log out and log back in to the instance

At this point you should be able to run docker without sudo.

Step 2: Run and configure Rancher

To install and run the latest version of Rancher (v0.32.0 at the time of writing), follow the instructions in the docs. In a few minutes your Rancher server should be up and ready to serve requests on port 8080. If you browse to http://YOUR_EC2_PUBLIC_IP:8080/ you will be greeted with a welcome page and a notice asking you to configure access. This is an important step to prevent unauthorized access to your Rancher server. Head over to the settings section and follow the instructions here to configure access control.

We typically create a separate environment for hosting all developer facing tools, e.g., Jenkins, Seyren, Graphite etc to isolate them from the public facing live services. To this end, we’re going to create an environment called Tools. From the environments menu (top left), select “manage environments” and create a new environment. Since we’re going to be working in this environment exclusively, let’s go ahead and make this our default environment by selecting “set as default login environment” from the environments menu.

The next step is to tell Rancher about our hosts. For this tutorial, we’ll launch all hosts with Ubuntu 14.04. Alternatively, you can add an existing host using the custom hostoption in Rancher. Just make sure that your hosts are running Docker 1.7.1+.

One of the hosts (JENKINS_MASTER_HOST) is going to run Jenkins master and would need some additional configuration. First, we need to open up access to port 8080 (default Jenkins port). You can do that by updating the security group used by that instance fom the AWS console. In our case, we updated the security group ( “rancher-machine” ) which was created by rancher. Second, we need to attach an additional EBS-backed volume to host Jenkins configuration. Make sure that you allocate enough space for the volume, based on how large your build workspaces tend to get. In addition, make sure the flag “delete on termination” is unchecked. That way, the volume can be re-attached to another instance and backed up easily:

Lastly, let’s add a couple of labels for the JENKINS_MASTER_HOST; 1) add a label called “profile” with the value as “jenkins” and 2) add a label called “jenkins-master” with the value “true”. We’re going to use these labels later to schedule master and slave containers on our hosts.

Step 3: Download and install rancher-compose CLI

As a last step, we need to install the rancher-compose CLI on our development machine. To do that, head over to the applications tab in Rancher and download the rancher compose CLI for your system. All you need is to add the path-to-your-rancher-compose-CLI to your PATH environment variable.

With that, our rancher server is ready and we can now launch and manage containers with it.

Launching Jenkins stack with Rancher

Step 1: Stack configuration

Before we launch the Jenkins stack, we need to create a new Rancher API key from API & Keys section under settings. Save the API key pair some place safe as we’re going to need it with rancher-compose. For the rest of the article, we refer to the API key pair as RANCHR_API_KEY and RANCHER_API_KEY_SECRET. Next, open up a terminal to fetch the latest version of Docker and Rancher Compose templates from Github:

Before we can use these templates, let’s quickly update the configuration. First, open up the Docker Compose file and update the Jenkins username and password to a username and password of your choice. Let’s call these credentials JENKINS_USER and JENKINS_PASSWORD. These credentials will be used by the Jenkins slave to talk to master. Second, update the host tag for slave and master to match the tags you specified for your rancher compute hosts. Make sure that the io.rancher.scheduler.affinity:host_label has a value of “profile=jenkins” for jenkins-slave. Similarly, for jenkins-master, make sure that the value for io.rancher.scheduler.affinity:host_label is “jenkins-master=true”. This will ensure that rancher containers are only launched on the hosts that you want to limit them to. For example, we are limiting our Jenkins master to only run on a host with an attached EBS volume and access to port 8080.

Once everything is running, find out the public IP of the host running “jenkins-lb” from the Rancher UI and browse to http://HOST_IP_OF_JENKINS_LB:8080/. If everything is configured correctly, you should see the Jenkins landing page. At this point, both your Jenkins master and slave(s) should be running; however, if you check the logs for your Jenkins slave, you would see 404 errors where the Jenkins slave is unable to connect to the Jenkins master. We need to configure Jenkins to allow for slave connections.

Configuring and Testing Jenkins

In this section, we’ll go through the steps needed to configure and secure our Jenkins stack. First, let’s create a Jenkins user with the same credentials (JENKINS_USER and JENKINS_PASSWORD) that you specified in your docker compose configuration file. Next, to enable security for Jenkins, navigate to “manage Jenkins” and select “enable security” from the security configuration. Make sure to specify 5000 as a fixed port for “TCP port for JNLP slave agents”. Jenkins slaves communicate with the master node on this port.

For the Jenkins slave to be able to connect to the master, we first need to install the Swarm plugin. The plugin can be installed from the “manage plugins” section in Jenkins. Once you have the swarm plugin installed, your Jenkins slave should show up in the “Build Executor Status” tab:

Finally, to complete the master-slave configuration, head over to “manage Jenkins”. You should now see a notice about enabling master security subsystem. Go ahead and enable the subsystem; it can be used to control access between master and slaves:

Before moving on, let’s configure Jenkins to work with Git and Java based projects. To configure git, simply install the git plugin. Then, select “Configure” from “Manage Jenkins” settings and set up the JDK and maven installers you want to use for your projects:

The steps above should be sufficient for building docker or maven based Java projects. To test our new Jenkins stack, let’s create a docker based job. Create a new “Freestyle Project” type job named “docker-test” and add the following build step and select “execute shell” with the following commands:

Save the job and run. In the console output, you should see the version of docker running inside your Jenkins container and the output for other docker commands in our job.

Note: The stop, rm and rmi commands used in the above shell script stops and cleans up all containers and images. Each Jenkins job should only touch it’s own containers, and therefore, we recommend deleting this job after a successful test.

Scaling Jenkins with Rancher

This is an area where Rancher really shines; it makes managing and scaling Docker containers trivially easy. In this section we’ll show you how to scale up and scale down the number of Jenkins slaves based on your needs.

In our initial setup, we only had one EC2 host registered with Rancher and all three services (Jenkins load balancer, Jenkins master and Jenkins slave) running on the same host. It looks like:

We’re now going to register another host by following the instructions here:

To launch more Jenkins slaves, simply click “Scale up” from your “Jenkins” stack in Rancher. That’s it! Rancher will immediately launch a new Jenkins slave container. As soon as the slave container starts, it will connect with Jenkins master and will show up in the list of build hosts:

To scale down, select “edit” from jenkins-slave settings and adjust the number of slaves to your liking:

In a few seconds you’ll see the change reflected in Jenkins list of available build hosts. Behind the scenes, Rancher uses labels to schedule containers on hosts. For more details on Rancher’s container scheduling, we encourage you to check out the documentation.

Conclusion

In this article, we built Jenkins with Docker and Rancher. We deployed up a multi-node Jenkins platform with Rancher Compose which can be launched with a couple of commands and scaled as needed. Rancher’s cross-node networking allows us to seamlessly scale the Jenkins cluster on multiple nodes and potentially across multiple clouds with just a few clicks. Another significant aspect of our Jenkins stack is the DIND containers for Jenkins master and slave, which allows the Jenkins setup to be readily used for dockerized and non dockerized applications.

In future articles, we’re going to use this Jenkins stack to create build pipelines and highlight CI best practices for dockerized applications. To learn more about managing applications through the upgrade process, please join our next online meetup where we’ll dive into the details of how to manage deployments and upgrades of microservices with Docker and Rancher.

Bilal and Usman are server and infrastructure engineers, with experience in building large scale distributed services on top of various cloud platforms. You can read more of their work at techtraits.com, or follow them on twitter @mbsheikh and @usman_ismail respectively.

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